U.S. patent number 4,810,076 [Application Number 06/866,585] was granted by the patent office on 1989-03-07 for selective shading device and an optical device using the same.
This patent grant is currently assigned to Matsushita Electric Industrial Co. Ltd.. Invention is credited to Kenichi Ikeda, Tsugio Murao, Yoshitomi Nagaoka, Yasuo Nakajima, Yoshiharu Yamamoto.
United States Patent |
4,810,076 |
Murao , et al. |
March 7, 1989 |
Selective shading device and an optical device using the same
Abstract
A selective shading device has a number of shading plates or
planar members and a supporting body that holds the plates or
planar members in such a manner that they are arrranged radially
with respect to an optical axis. The device blocks sagittal bundles
of rays. A preferred example of the supporting body is a
cylindrical frame that holds the shading plates perpendicularly to
the inner surface thereof. Alternatively, the shading planar
members are formed within a lens element along the edge
thereof.
Inventors: |
Murao; Tsugio (Habikino,
JP), Yamamoto; Yoshiharu (Toyonaka, JP),
Ikeda; Kenichi (Takatsuki, JP), Nagaoka;
Yoshitomi (Neyagawa, JP), Nakajima; Yasuo
(Ibaraki, JP) |
Assignee: |
Matsushita Electric Industrial Co.
Ltd. (Osaka, JP)
|
Family
ID: |
27313555 |
Appl.
No.: |
06/866,585 |
Filed: |
May 23, 1986 |
Foreign Application Priority Data
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May 31, 1985 [JP] |
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60-118328 |
Dec 13, 1985 [JP] |
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60-281347 |
Dec 13, 1985 [JP] |
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60-281352 |
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Current U.S.
Class: |
359/738; 359/227;
359/611 |
Current CPC
Class: |
G02B
5/005 (20130101) |
Current International
Class: |
G02B
5/00 (20060101); G02B 026/02 () |
Field of
Search: |
;350/252,266,268,276,276R,448,449,450,451,452,578,580 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
"Introduction to Optics", vol. 1, p. 123, published by
Asakura-shoten, Japan..
|
Primary Examiner: Corbin; John K.
Assistant Examiner: Kachmarik; Ronald M.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack
Claims
What is claimed is:
1. A selective optical shading device having an optical axis, and a
plurality of shading members for blocking sagittal rays and rays
close to sagittal rays of a light directed at the device, said
shading members disposed radially with respect to the optical axis,
and each of said shading members comprising a planar shape located
in a respective one of meridional planes along which the optical
axis extends, wherein for every blocked sagittal ray, the shading
members are designed to satisfy the relation:
where .omega. is an angle that a principal ray makes with the
optical axis; D is the portion of a sagittal ray that is cut by one
of the shading members when the sagittal ray is projected on a
plane which is vertical to the meridional plane and contains the
optical axis; L is the average distance between said portion of the
sagittal ray that is cut by one of the shading members and the
optical axis; .beta. is an angle that said sagittal ray when
projected makes with the optical axis; and .alpha. is an angle that
adjacent ones of the meridional planes in which the shading members
are located make with each other.
2. A selective shading device as set forth in claim 1, wherein the
shading members are equally angularly spaced apart from one another
by a distance extending in a direction around the optical axis and
satisfy the relation:
where N is the number of the shading members, and .alpha. is said
distance.
3. A selective shading device as set forth in claim 1, wherein the
shape of each of the shading members is a quadrangle.
4. A selective shading device as set forth in claim 1, wherein the
shape of each of the shading members is a rectangle.
5. A selective shading device as set forth in claim 1, wherein the
shape of each of the shading members is a trapezoid.
6. A selective shading device as set forth in claim 1, wherein the
shape of each of the shading members is a parallelogram.
7. A selective shading device as set forth in claim 1, wherein the
shading members are colored to absorb light.
8. A selective shading device having an optical axis, said device
comprising:
a plurality of shading plates for blocking sagittal rays and rays
close to sagittal rays of a light directed at the device, said
shading plates disposed radially with respect to the optical axis,
and each of said shading plates having a planar shape located in a
respective one of meridional planes along which the optical axis
extends; and
a supporting means for supporting said shading plates in position
relative to one another, the supporting means comprising a
supporting frame having a cylindrical inner surface on which each
of the shading plates is supported perpendicular to the inner
surface at respective first ends thereof.
9. A selective shading device as set forth in claim 8, further
comprising a reinforcing ring that fixes another end of each of the
shading plates.
10. A selective shading device as set forth in claim 8, and further
comprising an optical element disposed in an optical relationship
with said shading plates for forming an optical device.
11. A selective shading device comprising:
a base that transmits light, said base having an optical axis;
and
a plurality of shading members for blocking sagittal rays and rays
close to sagittal rays of light directed at the device, said
shading members disposed radially with respect to the optical axis,
and each of said shading members comprising a planar shape located
in a respective one of meridional planes along which the optical
axis extends, wherein for every blocked sagittal ray, the shading
members satisfy the relation:
where .omega. is an angle that a principal ray makes with the
optical axis; D is the portion of a sagittal ray that is cut by one
of the shading members when the sagittal ray is projected on a
plane which is vertical to the meridional plane and contains the
optical axis; L is the average distance between said portion of the
sagittal that is cut by one of the shading members and the optical
axis; .beta. is an angle that said sagittal ray when projected
makes with the optical axis; and .alpha. is an angle that adjacent
ones of the meridional planes in which the shading members are
located make with each other.
12. A selective shading device as set forth in claim 11, wherein
the base is cylindrical.
13. A selective shading device as set forth in claim claim 11,
wherein the base comprises a lens.
14. A selective shading device as set forth in claim 11, wherein
the base has slits each of which extends in a respective one of
said meridional planes, and said shading members comprise a medium
that absorbs light and is disposed in said slits.
15. A selective shading device as set forth in claim 11, wherein
the shading members are equally angularly spaced apart from one
another by a distance extending in a direction around the optical
axis and satisfy the relation:
where N is the number of the shading members, and .alpha. is said
distance.
16. A selective shading device as set forth in claim 11, wherein
the shape of each of the shading members is a quadrangle.
17. A selective shading device as set forth in claim 11, wherein
the shape of each of the shading members is a rectangle.
18. A selective shading device as set forth in claim 11, wherein
the shape of each of the shading members is a trapezoid.
19. A selective shading device as set forth in claim 11, wherein
the shape of each of the shading members is a parallelogram.
20. An optical device comprising:
an optical lens having an optical axis; and
a plurality of shading members for blocking sagittal rays and rays
close to sagittal rays, said shading members disposed radially with
respect to the optical axis, and each of said shading members
comprising a planar shape located in a respective one of meridional
planes along which the optical axis extends, wherein for every
blocked sagittal ray, the shading members satisfy the relation:
where .omega. is an angle that a principal ray makes with the
optical axis; D is the portion of a sagittal ray that is cut by one
of the shading members when the sagittal ray is projected on a
plane which is vertical to the meridional plane and contains the
optical axis; L is the average distance between said portion of the
sagittal that is cut by one of the shading members and the optical
axis; .alpha. is an angle that said sagittal ray when projected
makes with the optical axis; and .alpha. is an angle that adjacent
ones of the meridional planes in which the shading members are
located make with each other.
21. An optical device as set forth in claim 20, wherein the shading
members are integral with the lens.
22. An optical device as set forth in claim 20, wherein the shading
members comprise a plurality of shading plates, and further
comprising a supporting means for supporting said plates radially
with respect to the optical axis of the lens.
23. An optical device as set forth in claim 22, and further
comprising a means for moving the shading plates with respect to
the optical axis.
24. An optical device as set forth in claim 20, wherein the shading
members are equally angularly spaced apart from one another by a
distance extending in a direction around the optical axis and
satisfy the relation:
where N is the number of the shading members, and .alpha. is said
distance.
25. An optical device as set forth in claim 20, wherein the shape
of each of the shading members is a quadrangle.
26. An optical device as set forth in claim 20, wherein the shape
of each of the shading members is a rectangle.
27. An optical device as set forth in claim 20, wherein the shape
of each of the shading members is a trapezoid.
28. An optical device as set forth in claim 20, wherein the shape
of each of the shading members is a parallelogram.
29. A selective shading device having an optical axis, said device
comprising:
a plurality of shading plates for blocking sagittal rays and rays
close to sagittal rays of a light directed at the device, said
shading plates disposed radially with respect to the optical axis,
and each of said shading plates having a planar shape located in a
respective one of meridional planes along which the optical axis
extends;
a supporting means for supporting said shading plates in position
relative to one another; and
means for moving the shading plates relative to the optical
axis.
30. A selective shading device as set forth in claim 29, wherein
the supporting means comprises at least one transparent plate
extending perpendicular to the optical axis.
31. A selective shading devices as set forth in claim 29, wherein
the shading plates are equally angularly spaced apart from one
another by a distance extending in a direction around the optical
axis and satisfy the relation:
where N is the number of the shading plates, and .alpha. is said
distance.
32. A selective shading device as set forth in claim 29, wherein
the shape of each of the shading plates is a quadrangle.
33. A selective shading device as set forth in claim 29, wherein
the shape of each of the shading plates is a rectangle.
34. A selective shading device as set forth in claim 29, wherein
the shape of each of the shading plates is a trapezoid.
35. A selective shading device as set forth in claim 29, wherein
the shape of each of the shading plates is a parallelogram.
36. A selective shading device having an optical axis, said device
comprising:
a plurality of shading plates for blocking sagittal rays and rays
close to sagittal rays of a light directed at the device, said
shading plates disposed radially with respect to the optical axis,
and each of said shading plates having a planar shape located in a
respective one of meridional planes along which the optical axis
extends; and
a supporting means for supporting said shading plates in position
relative to one another, and wherein the shading plates satisfy the
relation:
where .omega. is an angle that a principal ray makes with the
optical axis; D is the portion of a sagittal ray that is cut by one
of the shading plates when the sagittal ray is projected on a plane
which is vertical to the meridional plane and contains the optical
axis; L is the average distance between said portion of the
sagittal that is cut by one of the shading plates and the optical
axis; .alpha. is an angle that said sagittal ray when projected
makes with the optical axis; and .alpha. is an angle that adjacent
ones of the meridional planes in which the shading plates are
located make with each other.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a shading device for use in an
optical system and also to an optical device equiped with the
shading device. More specifically, the invention relates to a
shading device for blocking only sagittal rays and also to an
optical device equipped with the shading device.
2. Description of the Prior Art
One means conventionally adopted to remedy aberrations of a lens is
to place a stop having a circular or substantially circular hole in
a plane perpendicular to the optical axis of the lens, the center
of the stop being located on the optical axis (for example, see
"Introduction to Optics", Vol. 1, p. 123, published by
Asakura-shoten, Japan).
Many kinds of lenses including Gaussian lenses exhibit very large
sagittal ray aberration. In order to reduce the aberration, a
circular stop has been inserted in the optical axis to reduce the
aperture, for blocking sagittal rays. However, this stop has the
disadvantage that the reduction in the aperture results in a
corresponding amount of axial and meridional rays being
blocked.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a shading
device capable of blocking only sagittal rays.
It is another object of the invention to provide an optical device
equipped with the shading device described above.
The shading device according to the invention has a plurality of
shading planar members extending in meridional planes containing an
optical axis.
Generally, off-axis sagittal rays intersect the plane which is
vertical to a meridional plane and contains the optical axis.
Accordingly, any shading plane substantially perpendicular to the
meridional plane stops sagittal rays, while meridional rays travel
in a direction extending along the meridional plane. Therefore, any
shading plane lying close to the meridional plane is substantially
parallel to the meridional plane, and does not block meridional
rays. Skewed rays other than meridional and sagittal rays are
blocked in larger amounts as they more closely approximate sagittal
rays, and are allowed to pass by a larger amount as they more
closely approximate meridional rays. In this way, only sagittal
rays and rays close to sagittal rays can be blocked.
The shading planar members can be comprised of a plurality of thin
plates (shading plates) held by a supporting means. Alternatively,
the shading planar members can be formed within a transparent solid
body. The shading plates or planar members are formed integrally
with a lens to form an optical device that can block only sagittal
rays.
The above and other objects and features of the invention will
become more apparent from the following description of the
preferred embodiments taken in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing an embodiment of a shading
device according to the present invention;
FIG. 2 is a diagram showing a relation of the shading device shown
in FIG. 1 to sagittal rays;
FIG. 3 shows various shapes that a shading plate according to the
present invention can take;
FIGS. 4(a)-4(d) are perspective views of other embodiments of a
shading device according to the invention;
FIG. 5 is a perspective view of a further embodiment of a shading
device according to the invention;
FIG. 6 is a cross-sectional view of a projection lens for use in a
projection television set, the lens incorporating the shading
device shown in FIG. 1;
FIGS. 7(a)-7(c) illustrate the principle on which a shading device
according to the invention operates in a projection television set,
as well as the effects of the device;
FIG. 8 is a perspective view of an optical element comprising a
lens in which shading planes are formed;
FIG. 9 is an exploded perspective view of a driving mechanism of
still another embodiment of a shading device equipped with movable
means according to the present invention;
FIG. 10 is a perspective view of yet another embodiment of a
shading device according to the invention;
FIGS. 11(a) and 11(b) are fragmentary perspective views of the
shading device shown in FIG. 10, showing manners in which the
device is fabricated .
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, there is shown a shading device embodying the
concept of the present invention. This device has a plurality of
thin opaque plates 1 (shading plates, hereinafter). The shading
plates 1 are held by a cylindrical supporting frame 2, and are
angularly equally spaced from one another and extend in a vertical
direction relative to the cylindrical inner surface of the
supporting frame 2. That is, the shading plates 1 are arranged on
meridional planes containing an optical axis, or the center axis of
the frame 2. The surfaces of the plates 1 and the inner surface of
the frame 2 are colored black, for example, for absorbing light to
prevent the incident light from being reflected therefrom. The
shading device shown in FIG. 1 has 18 shading plates 1.
The relation of the shading device shown in FIG. 1 to off-axis
sagittal rays will next be described by referring to FIG. 2, where
the meridional plane is indicated by plane YOO'. Plane ZOO' is
perpendicular to the meridional plane and contains the optical axis
OO'. A straight line 4 is an image obtained by projecting a
sagittal ray 3 onto the plane ZOO'.
Consider the case in which one of the shading plates 1 lies on the
plane ZOO'. The projected image 4 intersects the front and rear
edges of the shading plate at points Q and R, respectively. The
distance between the points Q and R is indicated by D. The midpoint
S of the line segment QR lies on the projected image 4. The line
segment normal to the optical axis OO' and intersecting the
midpoint S has a length of L (hereinafter referred to as "average
distance"). The projected image 4 makes an angle of ' with the
optical axis OO'. The principal ray 5 makes an angle of ' with the
optical axis OO'. The number of shading plates 1 is N. For every
blocked sagittal ray, the values of D, .beta., .omega., L, N are
determined to satisfy the following relationship:
The shading device designed as described above operates in the
manner described below. An axial bundle of rays is blocked by the
plate 1 by an amount corresponding to the area of the cross section
of the plate 1, but the reduction in the amount of light is small
because the plate 1 is thin. Similarly, a bundle of off-axis
meridional rays is blocked by the plate 1 also by an amount
corresponding to the area of the cross section of the plate 1. Also
in this case, the reduction in the amount of light is small.
Neighboring shading plates make an angle of 2.pi./N (radians) with
each other. The average interval between the neighboring shading
plates which is taken at the positions where sagittal rays
intersect the plates is approximately L sin (2.pi./N). The length
of the projected image 4 which is taken along the optical axis is D
cos '. The sagittal ray 3 travels a distance of D cos .beta. tan
.omega. in a radial direction while it passes across the shading
device. Accordingly, if the distance travelled by the sagittal ray
in a radial direction is equal to or greater than the average
interval between the shading plates 1, i.e., D cos .beta. tan
.omega..gtoreq.L sin(2.pi./N), then the sagittal ray is
blocked.
The blocked sagittal bundle is a set of sagittal rays as mentioned
above. Usually, sagittal bundles of various field angles are
stopped. Thus, the above relation (1) is fulfilled for every
blocked sagittal ray under the condition that .beta., .omega., L
are variables.
It is not necessarily required to equally space the shading plates
1 from one another angularly. Let .alpha. be the angle that the
neighboring shading plates make with each other. For the sagittal
ray that satisfies the relations .beta.=.beta..sub.1,
.omega.=.omega..sub.1, and L=L.sub.1, the distance D and the angle
.alpha. are determined to satisfy the following relation:
Then, the same effects will be produced as obtained where the
shading plates 1 are spaced from one another regularly. That is,
for a certain sagittal ray, if the value of D/sin .alpha. is the
same, the same effects are produced.
Any shape other than that shown in FIG. 1 can be employed for the
shading plate as long as it can satisfy the aforementioned
relation. For example, as shown in FIG. 3, the shape can be a
quadrangle (a), trapezoid (B), parallelogram (c), or rectangle (d).
However, as the difference between both sides of the above
relational formula becomes larger, more rays which are not required
to be blocked are stopped.
The shape of the supporting means for holding the shading plates 1
is not limited to the shape shown in FIG. 1. For instance, it may
be a truncated cone. Also, the supporting frame 2 may be replaced
by a supporting ring 6 as shown in FIG. 4(a) or radial supporting
spokes 7 as shown in FIG. 4(b). Furthermore, the supporting means
may be another optical element such as a lens 8 as shown in FIG.
4(c), where the optical axis is indicated by O-O'. Furthermore, the
shading plats 1 may be held circumferentially on at least one
transparent plate 50 extending perpendicular to the optical axis
O--O' as shown in FIG. 4(d).
As described above, the shading device according to the invention
does not block off-axis meridional bundles of rays, but stops
sagittal bundles of rays. By replacing the conventional stop
arranged to block off-axis sagittal bundles of rays with the novel
shading device, those meridional bundles of rays which heretofore
would have been blocked are allowed to pass through an optical
element, such as a lens. This makes the optical element remarkably
brighter.
Referring next to FIG. 5, there is shown another embodiment of a
shading device according to the invention. This device comprises a
plurality of shading plates 1 held by a cylindrical supporting
frame 2 and a reinforcing ring 9 that supports inner ends of the
plates 1. The parameters that determine the shape of each of the
shading plates 1 are illustrated in FIG. 2 in the same manner as
the shading device already described in conjuction with FIG. 1. For
every blocked sagittal ray, the parameters D, .beta., .omega., L,
and N are determined to satisfy the above-described relation (1).
The shading device constructed in this way operates in the same
manner as the shading device described above.
It is desirable to make the shading plates 1 as thin as possible so
that fewer axial bundles of rays are blocked. However, if they are
too thin, they will bend or twist, resulting in an equivalent
increase in cross-sectional area. Therefore, each shading plate is
reinforced by at least one ring 9 to minimize the bend or twist.
Hence, ideal shading plates can be achieved.
An optical device incorporating a shading device according to the
invention will next be described. Referring to FIG. 6, there is
shown a projection lens for use in a projection television set,
incorporating the shading device shown in FIG. 1. It is now assumed
that the projection lens exhibits large aberrations for off-axis
sagittal marginal rays. The shading device shown in FIG. 1 is
indicated by numeral 10 in FIG. 6. The projection lens consists of
lens elements 11, 12 and 13 which are held inside a lens barrel 14.
Preferably, the shading device 10 is located in a position at which
the principal ray of the blocked sagittal bundle of rays intersects
the optical axis O--O'.
The operation of the optical device incorporating the shading
device as shown in FIG. 6 will now be described. First, the
principle of operation of the projection television set will be
described by referring to FIG. 7(a), where a cathode-ray tube (CRT)
15, a screen 16, and a projection lens 17 are shown. A point light
source P' on the CRT 15 is projected on the screen 16, forming an
image P. The projected image P which is obtained when the shading
device is not present is shown in FIG. 7(b). Because of off-axis
sagittal marginal rays and skew rays near these sagittal marginal
rays, both of which are indicated by the dotted areas, the
projected image P is tailed in the sagittal directions. The
projected image P which is obtained when the shading device is
employed is shown in FIG. 7(c), in which the off-axis sagittal
marginal rays and the skew rays near these sagittal marginal rays
are blocked. The projected image P forms a point image in which the
sagittal and meridional aberrations are well balanced. Axial
bundles of rays and off-axis meridional bundles of rays are not
blocked substantially. As described thus far, in the present
invention, the image quality can be remarkably enhanced without
greatly impairing the brightness of the lens. While the projection
lens for use in the projection television set is constituted by the
present invention, the invention is also applicable to all optical
systems, including a camera, in which a lens gives rise to large
sagittal ray aberration.
An optical device comprising a lens in which shading planar members
according to the invention are formed will be described below.
Referring to FIG. 8, there is shown a lens 19 which is similar in
shape to the projection lens 11 shown in FIG. 6. The shading device
10 shown in FIG. 6 is unnecessary in this example. A plurality of
shading planar members 18 are formed in the lens 19. The shading
planar members are extend along meridional planes, and are equally
angularly spaced from one another about the optical axis O--O' of
the lens 19, the edge of which is indicated by numeral 20. The
shading planes 18 are blacked or otherwise colored to absorb light,
for preventing the reflection of the incident light therefrom. As
an example, the lens 19 is made from a plastic, and is notched at
the edge 20. Then, a black paint is injected into the produced
notches. In the example shown in FIG. 8, the number of shading
planar members 18 is eighteen. The parameters that determine the
shape of the shading planar members 18 are illustrated in FIG. 2 in
the same manner as in the case of the first-mentioned embodiment.
For every blocked sagittal ray, the parameters D, .beta., .omega.,
L, N are determined to satisfy the previously described relation
(1).
The shading planar members 18 designed as described above operate
in the same manner as the shading plates 1 shown in FIG. 1. It is
not required that the shading planar members 18 be equally
angularly spaced from one another. Let .alpha. be the angle that
neighboring shading planar members 18 make with each other. For the
sagittal ray conforming to the relations .beta.=.beta..sub.1,
.omega.=.omega..sub.1, and L=L.sub.1, the values of D and .alpha.
are determined to satisfy the previously described relation (2).
Thus, the same effects will be produced as obtained when the
shading planar members equally angularly spaced from one
another.
The shading planar members 18 may have any other shape than the one
shown in FIG. 8, as long as the aforementioned relationship is
satisfied. For example, as shown in FIG. 3, the shading members may
be a quadrangle (a), trapezoid (b), parallelogram (c), or rectangle
(d), in the same fashion as the first embodiment. Note that if the
difference between both sides of the formula becomes larger, then
more rays which need not be blocked are stopped.
As described thus far, the FIG. 8 embodiment constitutes an optical
device comprising a lens in which shading planar members for
blocking sagittal rays and for passing meridional rays are formed.
Axial bundles of rays and meridional bundles of rays which
heretofore would have been blocked are permitted to pass through
the optical device. Consequently, the optical device is rendered
remarkably brighter than the prior art device.
A shading device having movable means and fabricated in accordance
with the invention will next be described.
Referring to FIG. 9, there is shown a structure of a driving
mechanism according to the invention. The mechanism has a guide 21
that is integral with a shading plate 1. The mechanism further has
a fixed supporting frame 22, an inner movable supporting frame 23,
and an outer movable supporting frame 24. The supporting frames 23
and 24 are fixed to each other. The fixed supporting frame 22 is
provided with a groove 25 for guiding the shading plate 1. The
supporting frames 23 and 24 are provided with grooves 26 and 27,
respectively, which are surrounded by vertical flat walls, to guide
the shading plate 1. The movable frames 23 and 24 are held in a
movable ring 28. The fixed frame 22 has threaded portions 29. The
movable ring 28 has tapped portions 30. The supporting frames 22,
23, 24 and the movable ring 28 are all cylindrical in shape, but
only the portions which correspond to one shading plate are shown
in FIG. 9 for simplicity.
The outer surface of the inner movable supporting frame 23 and the
inner surface of the outer movable supporting frame 24 form a guide
groove that is at an angle to the center axis, or the optical axis
O-O'. When the ring 28 is rotated, it moves to and fro, insomuch as
its tapped portions 30 are in mesh with the threaded portions 29.
At this time, the movable supporting frames 23 and 24 move to and
fro along the optical axis while guided by the fixed supporting
frame 22. As a result, the shading plate 1 is moved up and down. A
guide hole 25 formed in the fixed supporting frame 22 acts to
restrict the movement of the shading plate to vertical movement.
The hole 25 also serves to retain the plate 1 in a way in which the
plate extends radially with respect to the center.
Referring to FIG. 10, there is shown a still another shading device
according to the invention. This device comprises a transparent
body 41 in which a plurality of shading planar members 40 are
formed. The transparent body 41 is made of glass or plastic. The
shading planar members 40 are arranged in the same manner as the
shading planar members already described. The shading device shown
in FIG. 10 has a advantage in that the shading planar members 40
can be made quite thin. As shown in FIG. 11(a), slits 42 are formed
at the periphery of the transparent body 41, and then a
light-blocking paint is injected into the slits to form the shading
planar members 40. Alternatively, as shown in FIG. 11(b),
transparent elements 43 (only one is shown) each having a
light-blocking coating 44 at least on a part of its one side
surface are stuck to each other in a side-by-side relation.
Obviously, by shaping the transparent body 41 shown in FIG. 10 into
a lenticular form, the optical device shown in FIG. 8 can be
derived.
Although some embodiments have been described, various other
changes and modifications can be made within the scope of the
invention which is solely defined in the appended claims.
* * * * *